1. Field of the Invention
The present invention relates to an RPR (Resilient Packet Ring) network constituted in such a way that a plurality of RPR devices are connected to one or more rings, and more particularly to a packet transfer method using an RPR technique that uses an L2-RPR mapping table in a layer 2 (L2, namely datalink layer in OSI reference model)
2. Description of the Related Art
Conventionally, in a connection between remote hosts, network construction using a private line was a typical method. However, in the network establishment using the private line, in an end-to-end communication, the following problems occur.    (1) This results in the occupation of all bandwidths.    (2) A price is set high in various services such as private line IP (Internet Protocol) connection and the like.
Also, because of its system in which the price of services are determined on the basis of a connection distance of the private line, the construction of a national network based on the private line requires a large amount of money.
To that end, in order to solve the problems of the network establishment based on the private line, the technique proposed under the assumption that the LAN (Local Area Network) technique used on the user's side is used to establish all networks is a wide area LAN service.
The wide area LAN service is such that a method used in the LAN, namely, the Ethernet (registered treadmark) used in the network, in which computers at positions relatively close to each other are connected, is expanded and applied to a large-scale wide area network service (see FIG. 37).
The user takes a merit that since all hosts seem to be simply connected through the LAN, it is very easy to use, and an apparatus cost and a maintenance cost are low. Due to those facts, the wide area LAN service is wide-spreading now.
In the current wide area LAN service, a connection point to the user can be attained through a cheap LAN interface. However, the interface inside a carrier network is attained (realized) by mapping a frame of the Ethernet (IEEE 802.3) to a SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy) technique having a high reliability. This SONET/SDH neither occuping the bandwidth nor obtain a statistic multiplex effect. For this reason, the usage fee of the SONET/SDH is very high for the user.
In such situation, the RPR technique appears as a technique replacing the expensive SONET/SDH communication portion. The RPR uses a packet ring (ringlet) accessing method, which enables data communication with the bandwidth from the minimum level of 155 Mbps to the maximum level of 10 Gbps. Also, since the RPR supports a double ring circulating in two opposite directions referred to as an outer ring and an inner ring, this is superior even in recoverability through trouble recovering means.
Moreover, in the RPR, while the merit of the packet communication is used to exhibit the statistic multiplex effect, similarly to the SONET/SDH, the bandwidth guarantee similar to a hard wired private line is established. Also, a data packet can be transmitted to both of the outer ring and the inner ring.
A transmission node has a function of transmitting data by selecting the side, which enables the shortest route, by using a topology detection technique when the data packet is transmitted. In this function, an RPR header is added to the transmission data packet at an inlet to the ring, and the RPR header is removed at an outlet from the ring.
Under the current situation, by installing the RPR function in a router having the L3 (layer 3, namely, network layer in OSI reference model) function such as a routing protocol or the like, the RPR device (node) is configured, and such an RPR device is used to establish the RPR ring network. That is, the RPR ring network under the current situation is attained with the L3 function given thereto. FIG. 38 is a principle explanatory view of the conventional RPR device.
The RPR device has interfaces for dropping in and dropping out from/to the outer ring and the inner ring and also has a plurality of user device interfaces.
Also, the RPR device includes: a transmission ring selector for selecting a transmission destination of a frame from the outer ring and the inner ring; a transmission RPR device judgment unit for judging an RPR device as the transmission destination of the frame; a reception user data judgment unit for analyzing the user data received from the user device interfaces; a user address learning unit for registering the correspondence between a user device address and its inclusioin (accommodated) position in a user device address/accommodation position learning table; a reception data judgment unit for analyzing the frame received from the RPR ring; a transmission position judgment unit for judging a transmission position of the frame to the user device; a user address retrieving unit for referring to the user device address/accommodation position learning table and retrieving an accommodation position corresponding to the user address; and an IP routing controller for carrying out routing of an L3 level to the received frame and a route selection.
In the RPR ring network under the current situation, the operation of the RPR device when a data transfer is executed from a terminal A to a terminal B is explained in brief with reference to FIG. 39. Respective numerals in the parenthesis in FIG. 39 related to the following outline correspond to numerals as below.
(1) A maintenance person carries out initial settings of RPR devices I to IV constituting the ring.
(2) Each of the RPR devices I to IV executes the ring topology detection and creates a topology map (the RPR device I collects the information on the node and the number of hops on the ring.
(3) Each RPR device and each router create the routing table in accordance with the routing protocol.
(4) The terminal A transmits an ARP (Address Resolution Protocol) request into a subnet to which the terminal A itself belongs (in order that the terminal A knows a MAC (Media Access Control) address of a router X).
(5) The router X transfers an ARP response to the terminal A (the terminal A recognizes a destination MAC address).
(6) The terminal A transmits a packet addressed to the terminal B to the router X (DA (Destination Address): the MAC address of the router X, SA (Source Address): the MAC address of the terminal A).
(7) The router X extracts the destination IP address from the reception packet and recognizes that the terminal B exists forward of the RPR device I, from the routing table created on the basis of the L3 routing protocol. Thus, the ARP request is sent into the subnet on the RPR device I side (in order that the router X knows the MAC address of the RPR device I).
(8) The RPR device I recognizes that the router X exists under the administration of a port “a” of the RPR device I itself (the RPR device I creates a MAC learning table (the user device address/accommodation position learning table)).
(9) The RPR device I transmits the ARP response to the router X (the router X recognizes the destination MAC address (the MAC address of the RPR device I)).
(10) The router X transmits the packet to the RPR device I (DA: the MAC address of the RPR device I, SA: the MAC address of the router X).
(11) The RPR device I extracts the destination IP address from the packet received in the step (10) and recognizes that the terminal B exists forward of the RPR device III, from the routing table. Thus, an RPR header (DA: the MAC address of the RPR device III, SA: the MAC address of the RPR device I) is added to the reception packet, and it is transmitted into the RPR ring.
(12) The RPR device II passes the packet therethrough because the packet destination is not the RPR device II, and the RPR device III drops the packet.
(13) The RPR device III transmits the ARP request into the subnet to which the terminal B belongs (in order that the RPR device III knows the MAC address of the terminal B).
(14) The terminal B transmits the ARP response to the RPR device III (the RPR device III recognizes the destination MAC address (the MAC address of the terminal B)).
(15) The RPR device III removes the RPR header of the received packet and transmits it to the terminal B (DA: the MAC address of the terminal B, SA: the MAC address of the RPR device III).
Incidentally, Luminous Networks Inc. provides a ring transmission technique “Resilient Packet Transport” (RPT) that can establish the ring type network such as the SONET/SDH by using the L2 technique. This technique is attained by using an encapsulation control based on a special frame format.
Also, as the technique provided originally prior to the standardization of IEEE802.17 as a different technique from the RPT, there are SRP (Spatial Reuse Protocol) of Cisco Systems Inc. and OPTera PacketEdge of Nortel Corporation. However, both the SRP and the OPTera PacketEdge are based on the control method with the L3 function given thereto.
Note that, as the prior art document related to the present application, there are the inventions noted in Patent Documents 1 and 2 below. Patent Document 1 discloses the technique for generating VPN (Virtual Private Network) on a shared network and creating an L2 routing table by mapping VLAN (Virtual Local Area Network) and MPLS (Multi-Protocol Label Switching) header in a network in which a communication is carried out inside the VPN.
Patent Document 2 discloses the technique for carrying out the packet transmission inside the ring without using capsule and token, by creating a table to carry out self-learning with respect to one or both of a ring side port and a local side port, in the network of the ring configuration.
[Patent Document 1]
JP 2002-164937 A
[Patent Document 2]
JP 2002-523992 A
The above-mentioned conventional RPR control method has the following problems (subjects). Firstly, in the current situation, the RPR function is installed in the router having the L3 (layer 3) functions such as the routing protocol so that the RPR device is configured, and such the RPR device is used to establish the ring network.
For this reason, required are a high performance CPU (Central Processing Unit) and high functional software and hardware. Also, the routing protocol requires a large-capacity memory. Those requirements cause the higher cost of the entire RPR device (node).
Secondly, since the RPR device is equipped with the L3 function, the expensive maintenance cost is required to operate/manage the complex function.
Thirdly, the method of realizing the objective one with the L2 function in the existing technique is attained by encapsulating the header by using the unique header and the like, such as Luminous Networks Inc. Thus, it could not be directly connected to the RPR device.